There are digital microscope apparatuses and viewers that use a microscope apparatus for observing a cellular tissue slide (preparation) to store slide information as digital images and perform a pathological diagnosis and the like using image data of the digital images.
The digital microscope apparatus enlarges the cellular tissue slide using an enlarging optical system to project the cellular tissue slide on an image sensor, takes images, and stitches (combines) a plurality of images, to form a single huge sample image.
At that time, since the depth of field of the microscope apparatus is very shallow (approximately 1 μm), in the case where a thick cellular tissue is photographed, photographing should be performed at a position (Z position), in an optical axis direction, at which an in-focus state becomes the best. Since the cellular tissue on the slide has irregular waves, an optimal focal position differs depending on the parts of the cellular tissue. Therefore, it is ideal to adjust a focal position each time photographing is performed.
The digital microscope apparatuses include, in order to automatically adjust a focal position, microscope apparatuses that adopt a contrast autofocusing (hereinafter, abbreviated to AF) system and microscope apparatuses that adopt a phase difference AF system.
For example, an AF system shown in Patent Document 1 is characterized by using, when a point at which contrast becomes the maximum is searched for, a difference between the last contrast value and a current contrast value to set the magnitude of the difference as a threshold value, and specifying an in-focus position using the threshold value. Further, in an AF system shown in Patent Document 2, the definition of a feature amount representing contrast includes hue information. In an AF system shown in Patent Document 3, the definition of a feature amount representing contrast adopts the amount of high-pass components.
Patent Document 1: Japanese Patent Application Laid-open No. 2007-86596
Patent Document 2: Japanese Patent Application Laid-open No. 2009-59326
Patent Document 3: Japanese Patent Application Laid-open No. Hei 03-258171